Protozoal diseases are serious diseases that remain unresolved. For example, leishmaniasis is an arthropod-borne zoonosis transmitted by sand flies, and is a protozoal disease transmitted to animals by animals for which 100 or more types of vertebrates can act as the reservoir host. Dogs and rodents have a particularly important role in transmission to humans, and the number of infected patients is as many as 12 million people in 88 countries, with 350 million people being exposed to the danger of infection. In recent years, the number of patients is showing an increasing trend, with approximately 2 million new incidences per year, and a severe outbreak has been confirmed in Afghanistan, with 200,000 or more people afflicted, including refugees. Leishmania are obligate intracellular protozoan parasites that multiply inside macrophages, and there are 20 or more species known to infect humans. Clinical symptoms in humans can be broadly classified into three groups, with visceral infection being potentially fatal as a result of a disturbance of hematopoiesis, whereas the unsightliness of skin lesions caused by cutaneous and mucocutaneous infections can cause enormous psychological distress. The majority of patients suffering from visceral leishmaniasis, which is the most serious form of the disease, are observed in developing countries, with 90% or more of incidences found within the four countries of India, Bangladesh, Brazil and Sudan. As a result of these circumstances, the WHO has placed leishmaniasis within the category of emergent and uncontrolled tropical infectious disease (category I), and has designated leishmaniasis as one of the ten major tropical infectious diseases requiring urgent measures.
Numerous compounds having unique structures that exhibit high bioactivity have been discovered from marine invertebrates, and they hold much promise as a source of medicines (Patent Document 1). The inventors of the present invention performed antiprotozoal activity screening of marine organisms collected in Japan, with the aim of developing an effective remedy for leishmaniasis. As a result of this screening, they discovered that Acanthoprimnoa cristata collected from deep sea locations contained an antiprotozoal substance. The present invention was completed on the basis of this discovery.